The present invention related to a field of art relating to a control device of a diesel engine.
Conventionally, diesel engines provided with a diesel particulate filter (hereinafter, referred to as the “DPF”) in an exhaust passage have been well known. The DPF captures particulate matters (PM) within the exhaust gas, and when an accumulation amount of the particulate matters increases, it needs to be regenerated. Normally, on the upstream side of such DPF, an oxidation catalyst is provided and a catalyst therein is used in the DPF regeneration. For example, JP2004-0316441A discloses a diesel engine that performs a main injection in which fuel for generating torque is injected into a cylinder, and then a post injection to introduce uncombusted fuel to an exhaust passage. When the uncombusted fuel reaches the catalyst, it is oxidized and increases an exhaust gas temperature. As a result, the PM accumulated in the DPF is combusted to be removed by a high temperature exhaust gas. Thus, the DPF is regenerated.
Meanwhile, when the engine is in a deceleration state, normally, the fuel injection to a cylinder on compression stroke (main injection) is prohibited (because a fuel cut is performed), and therefore, the temperature of the exhaust gas to be supplied to the oxidation catalyst significantly decreases, causing difficulty in maintaining the oxidation catalyst in an activated state. Therefore, even if the post injection is performed to regenerate the DPF, the injected uncombusted fuel will not be oxidized, and thus, an exhaust gas temperature increasing effect using heat from the oxidation reaction is lost and it takes time to regenerate the DPF, causing a degradation in fuel consumption and problems that a larger amount of fuel adheres on an in-cylinder wall face because the post injection and engine oil is diluted.